Mercury pollution in two gold mining areas of the Brazilian Amazon

Gold has been exploited intensively in the Brazilian Amazon during the past fifteen years using garimpo methods (small-scale gold mining). In this study, two gold mining areas were investigated, the municipalities of Pocone and Alta Floresta located in the state of Mato Grosso. Central Brazil. The elemental mercury (Hg) used in amalgamating the gold, the final stage of the ore dressing process, has caused abnormal Hg concentrations in waterways. This has occurred principally in the Amazon region, where most of the ore prospected is alluvial. Background levels of metals were determined by analyzing sediments and soils located upstream of the anthropogenic inputs and unaffected by mining activities. The study aimed to evaluate the pollution level in sediments and soils, taking into account drainage waters directly affected by gold mining. ‘Geoaccumulation indexes’ (Igeo) of Hg in sediments from both study areas were used to assesses the pollution level in the aquatic environment. The geoaccumulation indexes of Hg in sediments of the Bento Gomes River in Pocone indicate a relatively high degree of pollution at some sites, even reaching class 4 (1.85 mg/kg). However, when the river reaches the Pantanal swamp, Hg concentrations drop considerably to 0.30 mg/kg. This drop seems to be due to accumulation of metals in the sediments of a lake (sampling site PG-24), which retains most of the sediments transported by the Bento Gomes River. Accumulation of metals in the lake also occurred for Cu, Pb, Zn, Fe and Mn. In the region of Alta Floresta, total Hg concentrations in sediments of the Teles Pires River were studied in the grain size fractions < 74 μm and > 74 μm. Hg concentrations in bottom sediments of this river were higher than those found in the Pocone region, with increases of 1.5 to 30 times the background, and thus reaching an Igeo up to class 5.     

Temporal trend of the suspended sediment transport of the Amazon River (1984–2016)

ABSTRACT

We discuss the claim that the Amazon River has been subjected to a noticeable increase in suspended sediment transport (SST) in response to both climate and land-use changes. To study this, both satellite imagery and in situ data were compiled to produce a 32-year time series (1984–2016) of suspended sediment concentration. Both parametric and nonparametric statistics were applied to examine the SST time trend. The results indicate that there has been no statistically significant increase in SST in the last 32 years, independent of the statistical approach. The results indicate that, over the last 32 years at the Óbidos station, in Brazil, a recurring pattern of increase and decrease in SST has occurred, rather than a unidirectional systematic trend. This further explains the increasing trend reported in the literature and indicates that short time series are not recommended for time trend analyses due to the large inter-annual variability.     

Sediment hosted lead–zinc deposits of the Neoproterozoic Bambuí Group and correlative sequences, São Francisco Craton, Brazil: A review and a possible metallogenic evolution model

The Proterozoic sediment-hosted Zn–(Pb) sulfide and non-sulfide deposits of the São Francisco Craton, Brazil, are partially syn-diagenetic and epigenetic and were probably formed during extensional events. The majority of the deposits occur within shallow water dolomites. The Pb isotopic data of sulfides are relatively homogeneous for individual deposits and plot above the upper crust evolution curve of the Plumbotectonic model. Some of the deposits are characterized by highly radiogenic lead (²⁰⁶Pb/²⁰⁴Pb ≥ 21) originating from the highly radioactive crust of the São Francisco Craton. Pb and S isotopic data suggest the sources of metal and sulfur for the deposits to be the basement rocks and seawater sulfates in the sediments, respectively. The relatively high temperatures of formation (100 to 250 °C) and moderate salinity (3% to 20% NaCl equiv.) of the primary fluid inclusions in the sphalerite crystals suggest the participation of basinal mineralizing fluids in ore formation. The steep paleo-geothermal gradient generated by the radioactively enriched basement rocks probably assisted in heating up the circulating mineralizing fluids.     

Multiple Iron-Rich Spinel Phases and Hematite in a Magnetic Soil Developing on Tuffite

A dusky red Latosol developing on tuffite was examined in detail in order to characterize its iron oxide mineralogy. Magnetic separation and selective chemical treatment were employed. The mineralogical analyses were carried out by powder X-ray diffraction and Mössbauer spectroscopy, with the electron microprobe technique being used to assess the chemical composition of selected grains. Results reveal that iron-rich spinel-structure phases from this pedosystem are rather variable in chemical composition and lattice parameters, and can be grouped in at least three major populations: the first group consisting of the iron-richest phase, with very low Ti and Cr and virtually no Mg content and high Al; the second group presenting Ti>Mg>>Al>Mn contents but no Cr and the third group related to the Mg-richest phase with Mg>Ti>>Al>Mn. Two major populations of hematite were also identified: one with ～15 mol% Al and other practically Al-free. The first group is thought to be a product of neoformation in an Al-rich pedogenic medium whereas the second is likely to be transformed directly from maghemite. Though chemical treatment along with physical techniques provide a powerful way to characterize iron oxides of tropical soils, some methodological difficulties still remain, particularly those concerned with (i) the characterization and quantification of maghemite in presence of relatively large amount of hematite in the soil mixture, particularly by Mössbauer spectroscopy, and (ii) the allocation of the isomorphous substituents for iron in the cation sites of the spinel structure. Possible mechanisms of alteration of iron-rich phases in this pedosystem are discussed.     

Managing Technological and Financial Uncertainty: A Decision Science Approach for Strategic Drilling Decisions

This paper presents a framework to improve the quality of investment decisions in petroleum. The model presented enables the decision-maker to explicitly consider two major objectives when evaluating new petroleum opportunities—financial and technological gain. We utilize MultiAttribute Utility Theory (MAUT) to consider simultaneously the technological challenges of petroleum exploration into the capital budgeting process of an exploration and production firm. The MAUT methodology presented in this work demonstrates that in some mature areas the advantages to exploration are restricted further only to financial gain, based upon the present economic potential of the basin. On the other hand, other seemingly less attractive areas, such as deep horizons in deep-water basins, may represent attractive targets for new exploration as a result of the interaction of financial gain and technological advancement. This advantage reflects the technological gain as a key factor for future operations for oil discoveries in areas with big geological potential. The model presented in this work enables the decision-maker to consider explicitly the risk and rewards associated with both financial and technological payoffs, the decision-maker's tolerance for those types of risks, and the relative importance of each of those objectives in the context of ongoing petroleum exploration decisions.     

Effects of Explicit Urban-Canopy Representation on Local Circulations Above a Tropical Mega-City

The Advanced Regional Prediction System (ARPS) is coupled with the tropical town energy budget (tTEB) scheme to analyze the effects of the urban canopy circulation over the metropolitan area of São Paulo and its interactions with the sea breeze and mountain-valley circulation in the eastern state of São Paulo, Brazil. Two experiments are carried out for the typical sea-breeze event occurring on 22 August 2014 under weak synoptic forcing and clear-sky conditions: (a) a control run with the default semi-desert surface parametrization and; (b) a tTEB run for the urban canopy of São Paulo. A realistic land-use database over the south-eastern domain of Brazil is used in the downscaling simulation to a horizontal grid resolution of 3 km. Our results indicate that ARPS effectively simulates features of the nighttime and early morning land-breeze circulation, which is affected by the surrounding hills and the nocturnal heat island of São Paulo. By early afternoon, the south-eastern sea-breeze circulation moves inland perpendicular to the upslope of the Serra do Mar scarp, which generates a line of moisture convergence and updrafts further inland. Later, the convergence line reaches São Paulo and interacts with the circulation arising from the urban heat island (UHI), which increases the moisture convergence and strength of updrafts. The surface energy balance indicates that the UHI is caused by large sensible heat storage within the urban canopy during the day, which is later released in the afternoon and at night. The simulations are verified with available radiosonde and surface weather station data, land-surface-temperature estimates from the moderate resolution imaging spectroradiometer, as well as the National Center for Atmospheric Research reanalysis databases. The three-dimensional geometry of the urban canyons within the tTEB scheme consistently improves the thermodynamically-induced circulation over São Paulo.     

Oxidative stress in the mussel Mytella guyanensis from polluted mangroves on Santa Catarina Island,Brazil

Digestive glands of the mangrove mussel Mytella guyanensis, collected at one non-polluted site (site 1) and two polluted sites (sites 2 and 3), were analysed for different antioxidant defenses, lipid peroxidation and DNA damage. Thiobarbituric acid-reactive substance (TBARS) and 8-oxo-7,8-dihydro-2'-deoxyguanosine levels were enhanced at the polluted sites. With the exception of superoxide dismutase, the activities of catalase and glutathione peroxidase were also higher at the polluted sites. Greater increases were observed in glutathione reductase, glutathione S-transferase and etoxyresorufine-O-deethylase activities at the polluted sites. Conversely, reduced glutathione content was higher at the control site. Trace metal contents in mussels collected at polluted sites were increased compared to the control site, and there were strong positive correlations between TBARS and Cu and Pb contents. M. guyanensis is routinely exposed to an oxidative stress condition at both polluted sites, and considering xenobiotic bioaccumulation in bivalve molluscs, the mangrove mussel represents an excellent bioindicator for environmental monitoring studies.     

Correction to: Observational Investigation of the Statistical Properties of Surface-Layer Turbulence in a Suburban Area of São Paulo,Brazil: Objective Analysis of Scaling-Parameter Accuracy and Uncertainties

Boundary-Layer Meteorology -     

Development of a drought vulnerability index using MCDM and GIS: study case in São Paulo and Ceará, Brazil

Natural Hazards - Although climate change vulnerability research in general has increased over the last decade, Latin American countries have more directed more limited efforts toward vulnerability...